1. Field of the Invention
The present invention relates to an air compressor for compressing air to be used by a pneumatic tool such as a pneumatic nailer and a method for controlling the same.
2. Description of the Related Art
An air compressor applied for the operation of pneumatic tools is generally designed so that as a motor rotates a crankshaft in the main body of the air compressor, a piston served by the crankshaft reciprocates within a cylinder according to the rotation speed of the crankshaft and compresses air supplied via an intake valve. Thereafter, the compressed air is discharged from the main body of the air compressor, through an air release valve and a pipe, to an air tank for storage. The compressed air stored in this tank can then be applied for the operation of pneumatic tools used for nailing.
Since air compressors are frequently employed outdoors, such as at construction sites or in locations whereat houses are constructed close together, the present inventors, based on various perspectives, determined that improvements were advisable. Thus, we performed research to evaluate the performance of air compressors under actual prevailing encountered in various situations, and as a result, to delineate the user requests and technical problems we encountered during our research, we decided to use the following categories.
(1) Noise Reduction
Since an air compressor includes a mechanism for converting the rotation of a motor into the reciprocal movement of a piston in a cylinder, the generation of considerable noise can not be avoided. Further, since a nailer that uses air compressed by an air compressor also generates noise while in operation, there is considerable noise pollution, and physical discomfort, in an area surrounding a construction site whereat both air compressors and pneumatic nailers are being employed. Thus, when such equipment is to be used early in the morning or late in the evening at locations whereat houses are constructed close together, the request for maximum noise reduction is expressed especially strong.
(2) Increased Power and Efficiency
Locations whereat air compressors are employed are not always in satisfactory power supply environments; on the contrary, air compressors are frequency used in environments wherein sufficiently high voltages can not be obtained because long cords, stretched from other locations, are employed to supply power, or in environments wherein a large volume of the compressed air is used because multiple tools are in use at the same time.
Therefore, occasionally, high power cannot be output by an air compressor, and when, for example, nailers are employed while the power output is insufficient, a so-called shallow nail holding phenomenon can occur and nails can not be set well in the material being processed.
Usually, air is stored in the air compressor air tank at a pressure of from 26 to 30 kg/cm2, and during a period wherein no tools are being employed, air leakage can not be avoided. Thus, dependant on the air usage, a reduction in efficiency occurs.
(3) Improvement in Size Reduction and Portability
While some of the air compressors are used for pneumatic tools are of a stationary type, most air compressors are portable, and can be carried to and employed at construction sites. Therefore, a need has been expressed for minimum sized air compressors for which the portability is excellent. Thus, for compressed air generators, and drive portions therefor, complicated structures should be avoided, and to the extent possible, deterioration of portability should be prevented.
(4) Extension of Service Life
The service life of air compressors for supporting pneumatic tools is shorter than the service life of compressors used for refrigerators and air conditioners. This is understandable, when the severe environmental conditions under which air compressors are used are taken into account. However, longer service life is still demanded that can be attained by restricting, to the extent possible, load fluctuation, or by preventing the unnecessary compression of air.
(5) Suppression of Temperature Rise
Due to the reciprocal movement of a piston in a cylinder and the current flowing to a motor that indirectly drives the piston, an increase in the temperature within an air compressor is unavoidable. However, as the temperature in the air compressor is increased, loss is also increased, and the attainment of high efficiency is prevented. Therefore, a strong demand also exists for the suppression, as quickly as possible, of a rise in the temperature within an air compressor.
In JP-A-2002-228233, a technique is disclosed whereby an uncomfortable sensation is reduced by suppressing a difference in the noise that is generated during the continuous operation of an indoor fan motor for an air conditioner.
In JP-B-6-63505, an air compressor is disclosed wherein, in accordance with a pressure change state wherein, because of a reduction in the pressure in a tank, the air compressor begins a loaded operation, the operating mode in the standby state, following the increase in the pressure, is changed to a intermittent operating mode or a continuous operating mode.